In a case where, for example, an object on a roller conveyor is moved by being pushed with the conventional so-called motor-operated cylinder, the weight of the object, the resistance caused by the static friction of ball bearings acting on the rollers, and a load (reaction) to accelerate the object to a given speed, are applied simultaneously to the front end of the retractable rod of the cylinder when the object starts to be moved. Since the resistance caused by the static friction of the ball bearings acting on the rollers when the movement of the object starts is far greater than that caused by the dynamic friction of the ball bearings acting on the rollers during the movement of the object, a significant load is applied to the retractable rod of the motor-operated cylinder when the object starts moving. As a result, there is a problem in that the threaded part of the thread mechanism quickly wears away, so that in general the life of the motor-operated cylinder shortens.
This invention was made considering the above circumstances. Its purpose is to provide an improved motor-operated cylinder, wherein only the least possible load is applied to the thread mechanism thereof when an object to be moved starts moving.